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Re: Working on glossary

From: Martyn Horner <martyn.horner@profium.com>
Date: Wed, 12 Sep 2001 13:46:22 +0200
Message-ID: <3B9F4B0E.5F87025F@profium.com>
To: pat hayes <phayes@ai.uwf.edu>
CC: Graham Klyne <Graham.Klyne@MIMEsweeper.com>, w3c-rdfcore-wg@w3.org
Since I contributed last, Pat and Graham have been going at it

GK: http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Sep/0127.html
PH: http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Sep/0130.html
GK: http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Sep/0131.html
PH: http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Sep/0132.html
GK: http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Sep/0061.html

I am grateful for the attention paid to this question.

But, chaps, what I wanted to make was a glossary for the layperson which
would help their initial understanding of some of our terms. I see,
again, how dubious some of these terms are.

Pat knows, from an exchange which came to nothing probably because I
didn't express myself that well, that I am concerned about what I call
the `temporal coherence' of stuff `on the Web'. This does seem to be an
issue and, I can see, it's an issue which will not disappear just by
defining (and redefining) the words we use. We have to offer to the
newcomer a definition which allows for temporal variance without
completely denying the usefulness and significance of the words.

For those who haven't been following the thread, much of what has flowed
past has been about the validity of defining a resource at all given its
changing nature (whether incidentally in a changing world or
functionally as a news service, for instance). Graham initially wanted
to point out how separated the ideas of entity and resource were as in,
for example, `today's weather forecast'. Then the discussion started...

Just to quote some of GK's and PH's dialogue:

Graham refers me (usefully, thanks) to
http://www.w3.org/DesignIssues/Fragment.html where a distinction is made
between a fragmentid-less URI which refers to a generic document and a
fragmentided URI which refers to an identification within that document
(and not just, as we know, a point in that document :-). Thus no '#'
suggests just generic access and a '#' suggests an identification (eg,
of a resource). Then he says:

GK: `I find it difficult to unify the RDF idea of a resource (a thing
that is identified) with the general Web idea of a resource (a thing
that is queried or accessed) in light of these comments.'

Me: So do I, Graham. So do I. I also find it difficult to generalize
this distinction to non-document resources (you know the list, people,
organisations, trees in the park, numbers,...)

GK: (on the time-variance track) `The approach that I have seen adopted
is to treat such things as sequences of values, or time-varying
functions.' ... `Then, the resource can correspond to the current
weather forecast, but its extension includes the set of all weather
forecasts for all times;  the particular member of that extension one
retrieves depends on when the retrieval is performed.'

Me: Yes. This is why I think it's important to say that a `resource' is
an entity identified by need (if you like), that the act of identifying
it as a resource includes an understanding of such characteristics. This
may not be its most precise definition but it would suggest for a new
reader the role of the concept.

PH: `As I understand it, the real-world objects *are* resources, so the
idea of being retrievable on the web simply isn't applicable to
resources in general.'

Me: Retrievability is a characteristic of some resources, of course, but
is not the crucial aspect of their identification even if the identity
of a resource (`today's weather forecast') is expressed in terms of its
retrieval. The resource is identified as `today's weather forecast' and
its usefulness (the `need' for identification) is in its timeliness BUT
the act of retrieval is not what makes it a resource.

GK: `The alternative view I'm trying to offer here is that real-world
objects are not resources, per se.  In addition to the octet-sequences
that are web-retrievable entities, I'm suggesting that the real world
objects are 
(also) part of the resource extension I mentioned previously, rather
than the resource directly.'

GK: `... but such (time-sensitive) semantics would be part of the
semantics of a resource, about which the RDF model theory you have
described seems to be agnostic.'

Me: Ah-ha! Yes. This is how I think of it. The timeliness of information
belongs in the semantic of that information but should not, in some
sense, invalidate the identification of it as a resource. Again, a
resource is an entity identified as required: the semantics may suggest
that the entity will change.

PH: `In the meantime however we could also just put this issue off to
the future, and the current MT be thought of as kind of instantaneous
time-slice of this extended temporal semantics.'

Me: Oh, please, no. Or at least, let me get my glossary done with a nice
clear message for the newcomer while we perhaps agonize about the real
meanings. I don't think we have forced ourselves to consider that RDF
refers to `a time-slice of an extended temporal semantic'...

The ref
that Graham includes is a good one, I admit. The idea of a duri: URN
protocol to state that `I am referring to the page as it was then' is,
of course, a valid one but it does not fit in with the requirements of a
practical Semantic Web. Larry has it right but it's not going to help.
It's great for putting in legal documents. However, the Semantic Web is
going to have to cope with time-variant data and not just deliberately
time-variant (like today's weather) or with time-variance created by
retrieval or time-variance due to decay.

Help. What shall we tell the novice? `Resource' (and its relationship to
`entity') must be in the vocabulary of anyone starting to read the RDF
documentation. I'd have thought it completely reasonable that some
kernel of meaning can be attached to these words before such a reader
has to face that the `true' meaning has certain unclear aspects. 

Do my definitions suffice, I still wonder...

Martyn Horner <martyn.horner@profium.com>
Profium, Les Espaces de Sophia,
Immeuble Delta, B.P. 037, F-06901 Sophia-Antipolis, France
Tel. +33 (0) Fax. +33 (0)
Mob. +33 (0) Internet: http://www.profium.com
Received on Wednesday, 12 September 2001 07:46:10 UTC

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